計算佔用記憶體

    private static final long MEGABYTE = 1024L * 1024L;

    public static long bytesToMegabytes(long bytes) {
        return bytes / MEGABYTE;
    }

    public static void main(String[] args) throws Exception {
        runGC();

        long start = usedMemory();

        // Do Something ...

        long used = usedMemory() - start;
        System.out.println("Used memory is bytes: " + used);
        System.out.println("Used memory is megabytes: " + bytesToMegabytes(used));
    }

    private static final Runtime s_runtime = Runtime.getRuntime();

    private static long usedMemory() {
        return s_runtime.totalMemory() - s_runtime.freeMemory();
    }

    private static void runGC() throws Exception {
        long usedMem1 = usedMemory(), usedMem2 = Long.MAX_VALUE;
        for (int i = 0; (usedMem1 < usedMem2) && (i < 500); ++i) {
            s_runtime.runFinalization();
            s_runtime.gc();
            Thread.currentThread().yield();
            usedMem2 = usedMem1;
            usedMem1 = usedMemory();
        }
    }

​